One sector of the U.S. economy is thriving on the threat of a debt default apocalypse.

Survivalist industries -- from tactical training schools to doomsday bunker manufacturers -- are reporting an uptick in business over the past few days, as a first-ever U.S. default has inched closer to reality. The trend is seen from Virginia to Florida, California to Indiana.

"We're not quite Greece, but there's a realization we're moving slowly toward it," said Robert Allen, owner of Sigma III Survival School in Huntington, Ark. "Economic collapse is the most common cause of people wanting to start preparing."

Enrollment at Sigma, where clients learn how to be completely self-reliant, has surged in the past few weeks, Allen told ABC News. His customer base now tops 2,000, with many flying in from out of state. "Ninety percent of my customers are interested in the news and want to prepare their families for the worst," he said.

While experts say the odds of a doomsday default are low, and chance of a complete collapse of civilization out of the question, the fears many Americans harbor are very real. And they are perpetuated by a deepening distrust of government, experts say.

Only 19 percent of Americans in a Gallup poll last month said they trust government in Washington to do what is right always or most of the time. Eighty-one percent said they rarely, if ever, trust the government.

Survival trainers reached by ABC News said many of their clients are distrustful of government and fear a time will come soon when they'll have to go it alone, with the government bankrupt, U.S. currency worthless and the general public in a free-for-all.

"If the economy goes, it affects a far wider range of people than an isolated incident," said Richard Brown, CEO of Survival Concepts in Hamilton, Ind. "If you're in a hurricane or tsunami situation, you have some sense that forces from the outside will come to help you. That won't be the case if the dollar deflates or power across the country goes out.

"It's every one for him or herself," said Brown, who reports a spike in demand for his survival classes, which teach how to start a fire, find clean water, build a shelter and use weapons to protect oneself. "If you understand survival, you can be in a plane crash or economic collapse and it's no different."

In Weirsdale, Fla., northwest of Orlando, phones at the Byron Kerns Survival School were ringing off the hook on Monday. People were inquiring about classes to brush up on their fire-making and hunting skills because of concerns about an imminent default, Kerns told ABC News.

"People want familiarization in wilderness survival in the event of an economic calamity because the basics -- how to build a fire and how to make shelter -- are most important," he said. Classes at Kerns' school are booked through March.

The threat of a U.S. default has also been partly credited with triggering a recent spike in sales of survival gear, such as MREs (meals ready to eat), and security structures such as personal bunkers.

"We've seen a remarkable uptick in the past couple of weeks of inquiries on fortified homes," said Brian Camden of Harden Structures Inc., of Virginia Beach, Va. The structural engineering and construction firm specializes in disaster shelters and home security.

"There is a combination of uncertainties behind the surge, but all of them are connected to a possible economic collapse," Camden told ABC News. "There is much concern about one caused by a debt default or by a solar flare/EMP [electromagnetic pulse] that would wipe out the power grid."

Fortified homes are bulletproof, fireproof, self-powered and billed as able to repel outside attack. They have "active offensive and defensive components" to protect against anarchy in the case of economic chaos, Camden said. "Our customers' top priority is asset protection. And their families are their most important asset."

While U.S. officials and independent economists have not raised the specter of complete anarchy in the wake of a failure to raise the debt ceiling, they have used increasingly dire rhetoric to describe the consequences after Oct. 17. They warn a default could trigger economic shockwaves, send the dollar downhill, cause interest rates to soar and freeze credit markets across the globe. It could thrust the U.S. into a recession worse than 2008, some officials say.

"If there is that degree of disruption, that lack of certainty, that lack of trust in the U.S. signature, it would mean massive disruption the world over, and we would be at risk of tipping yet again into a recession," IMF head Christine Lagarde said on "Meet the Press" on Sunday.

Those warnings have plenty of average Americans on edge, and eager to stock up on water, practice fire-making skills and hunker down.